Method and apparatus for the vaporization of LPG utilizing infrared heat sources and heat exchangers

ABSTRACT

An apparatus and method for the vaporization of liquefied petroleum gas (LPG), having infrared burners  32 A and  32 B and primary and secondary heat exchangers  14  and  18 , respectively. A float switch  16  prevents the carryover of liquid into the produced LPG vapor stream. Fuel lines  24 A-C provide the burners with fuel, while burner panels  30 A and  30 B hold the burners in place. Pressure regulator  26  adjusts the pressure of the fuel line to the required burner fuel pressure. The primary heat exchanger is directly heated by infrared radiation, without the use of heat transfer media. The secondary heat exchanger increases the thermal efficiency of the vaporizer by recovering additional thermal energy that would otherwise be lost with the flue gasses.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable

FEDERALLY SPONSORED RESEARCH

Not Applicable

SEQUENCE LISTING OR PROGRAM

Not Applicable

BACKGROUND OF THE INVENTION

1. FIELD OF INVENTION

This invention relates to Liquefied Petroleum Gas (LPG) vaporizers,specifically a vaporizer utilizing infrared (IR) heat sources and heatexchangers.

BACKGROUND OF THE INVENTION

2. PRIOR ART

Vaporized LPG is primarily used in standby, backup, and peak-shavingsystems; in some instances, LPG is used as a primary fuel source insteadof natural gas. In low flow volume applications, LPG can be vaporized byrelying on the natural expansion that occurs when it is exposed toatmospheric pressure; however, this produces a refrigeration effect thatcan have deleterious consequences by freezing valves and burners in highflow volume applications. Vaporizers can be used to heat the LPG intovapor, which avoids the refrigeration effect.

Known designs of LPG vaporizers consist of three main elements: a sourceof heat, a vaporization tube, and a heat transfer medium to convey theheat from the source to the vaporization tube. Common sources of heatinclude burners, boilers (for steam and hot water vaporizers), andelectricity. Heat transfer media used in known designs of LPG vaporizersinclude water, water/glycol mixtures, steam, flue gasses (from burners),and metal (in electric vaporizers).

U.S. Pat. Nos. 4,203,300 and 4,131,084 to Hanson (1980 and 1978)disclose LPG vaporizers that utilize burners that heat an aqueoussolution, which in turn transmits heat to helical vapor tubes submersedin a water bath. Similar designs utilize tubes of hot water enclosing acentral heat exchanger or pressure vessel. The water bath separatespotential leaks of the flammable LPG from the heat source; therefore,these vaporizers are perceived by some users as safer than vaporizersthat use gaseous heat exchange media which do not offer this buffer. Themajor disadvantage of using liquid heat transfer media like water orwater/glycol mixtures is the inherent increase of density and thereforemass when compared to an equivalent volume of gaseous heat transfermedia like steam or flue gasses. This has the potential to limit therange of applications, since these installations tend to be large andheavy, therefore not easily moved or installed.

Another heat transfer medium option is the use of metal blocks, such asthe design for an electrical LPG vaporizer disclosed by U.S. Pat. No.4,645,904 to Moraski (1987). A number of electric resistance heatingelements heat aluminum blocks, which in turn transmit the heat to theLPG inside the vaporization tube. Though electric LPG vaporizers avoidthe need for fluid heat transfer media, the electric resistance heatingelements need powerful sources of electricity and are therefore notsuitable for installation and use in locations without easy access topower sources.

LPG vaporizer designs that rely on gaseous heat transfer media likesteam or flue gases tend to have smaller footprints and lower weightthan liquid media vaporizers. Burners used in LPG vaporizers of knowndesigns are often fueled by diverting a small portion of the vaporizedLPG, which makes the vaporizers independent from external fuel supplies.This greatly increases flexibility in placement and installation overelectrical designs. The major cause for consumer concern in the case ofvaporizers that utilize flue gasses or products of combustion as heatexchange media is the proximity of open flames to the vaporizationtubes. The possibility of an LPG leak directly into an environment withopen flames causes some users to perceive these designs as less safe;however, all known designs in current use are required to comply withthe regulations and guidelines of national agencies that havejurisdiction over the manufacturing, installation, and operation of suchdevices. In the U.S., these agencies include the American Society ofMechanical Engineers (ASME) and the National Fire Protection Agency(NFPA). A more realistic drawback is that gaseous media vaporizers tendto have lower flow capacities than liquid bath vaporizers, thoughsignificant overlap in capacities exists.

No new design for LPG vaporizers that uses a gaseous heat transfer mediahas been granted a patent in 30 years, though liquid bath vaporizershave been continually refined and redesigned for a number ofapplications. Nevertheless, all currently extant LPG vaporizer designssuffer from one or more of a variety of disadvantages and drawbacks:

a) Designs that utilize the direct application of an open flame to apressure vessel containing flammable LPG are perceived as less safe anddraw closer scrutiny by relevant authorities than designs utilizingnon-flame heat sources.

b) Liquid bath vaporizers have a longer startup time, since the bathneeds to be warmed before it can be used in vaporization.

c) Liquid bath vaporizers have a larger footprint and mass significantlymore than vaporizers that do not use a transfer medium.

d) Vaporizers that utilize multiple heat-exchange fluids ormulti-chambered and intricately connected pressure vessels increasecomplexity and cost of both manufacture and maintenance.

e) Significant energy of the flame is wasted as visible light that doesnot appreciably increase the energy input to the vaporization of LPG.

f) Electric designs require large-capacity power sources and are notsuitable for emplacement in locations where the existing infrastructuredoes not support such large electricity users.

BACKGROUND OF INVENTION—OBJECTS AND ADVANTAGES

Accordingly, several objects and advantages of the present inventionare:

a) to provide an LPG vaporizer that does not utilize the directapplication of flame to the pressure vessel or uses gaseous heattransfer media to vaporize the LPG;

b) to provide an LPG vaporizer that has a short startup time;

c) to provide an LPG vaporizer that is compact and light weight;

d) to provide an LPG vaporizer that provides for non-complex manufactureand maintenance; and

e) to provide an LPG vaporizer that makes efficient use of heat energy.

Further objects and advantages will become apparent from a considerationof the ensuing description and drawings.

SUMMARY

In accordance with the present invention an infrared vaporizer comprisesinfrared heat sources, heat exchangers, connecting piping and valves,controls, and an enclosure that holds individual components in place andprovides protection from external elements.

DRAWINGS—FIGURES

FIG. 1 is a perspective view of the invention, showing the enclosure andventing system.

FIG. 2 shows the same perspective view, with enclosure and ventingsystem removed to illustrate internal parts and systems, broadlyconsisting of infrared burners, heat exchangers, controls, andconnecting piping and valves.

FIG. 3 shows a rear view of the invention, with the enclosure removed,illustrating the interconnections of the various subsystems. DRAWINGS -Reference Numerals 10 enclosure 12 liquid inlet 14 primary heatexchanger 16 liquid carryover prevention switch 18 secondary heatexchanger 20 vapor outlet 22 fuel line valve 24 fuel line 26 pressureregulator 28 drip leg 30 burner panel 32 IR burner 34 burner controlvalve 36 hanging clamp 38 top clamp 40 pressure relief valve stack 42exhaust stack

Multiple instances of the same part are differentiated by lettersuffixes.

DETAILED DESCRIPTION OF THE INVENTION

The preferred embodiment of the present invention is illustrated inFIGS. 1 through 3. FIG.1 (exterior perspective view) shows an enclosure10, which surrounds and supports the major parts of the vaporizer, andallows for ventilation. Protruding from the enclosure is a liquid inlet12. An exhaust stack 42 vents the enclosure. A vapor outlet 20 providesvaporized LPG for use downstream of the vaporizer. The vapor outlet isalso connected to a fuel line valve 22, which takes off a small portionof LPG vapor to fuel the vaporizer. Also connected in line with thevapor outlet is a pressure relief valve stack 40.

FIG. 2 is a view of the vaporizer with the enclosure, pressure reliefvalve stack, and exhaust stack removed to show the interior (the base ofthe enclosure is shown).The fuel inlet connects to a primary heatexchanger 14. The primary heat exchanger connects to a liquid carryoverprevention switch 16, which is in line between the primary heatexchanger and a secondary heat exchanger 18. The secondary heatexchanger connects to the pressure relief valve stack and the vaporoutlet. The vapor outlet connects to the fuel line valve, which feeds afuel line 24A.

Burner panels 30A and 30B hold IR burners 32A and 32B in place,respectively, and act as thermal bulkheads. Hanging clamps 36A and 36Bhold the primary heat exchanger in place. Top clamps 38A-D secure thesecondary heat exchanger.

FIG. 3 shows a back view of the invention, again without the enclosure,the pressure relief stack, or the exhaust stack visible. The fuel linefrom the fuel line valve at the vapor outlet leads to a pressureregulator 26. Fuel lines 24B and 24C provide fuel to the IR burners. Adrip leg 28 protrudes down from the pressure regulator.

OPERATIONAL DESCRIPTION OF THE INVENTION

The operation of the vaporizer is performed as follows. After applyingcontrol voltage, a solenoid valve at the liquid inlet 10 opens andadmits LPG into the primary heat exchanger 14 from an LPG storage tank.The level of liquid begins to rise inside the liquid carryoverprevention switch 16, causing the liquid carryover prevention switch tointerrupt control voltage to the solenoid valve at the liquid inlet,causing the solenoid valve to close. A temperature switch at the vaporoutlet 20 senses that the outlet temperature is below the specifiedoperating range required for vaporized LPG and opens the burner controlvalves 34A and 34B on the IR burners 32A and 32B. The IR burners emitinfrared radiation, which directly heats the primary heat exchanger andthereby the LPG. The LPG begins to expand and the overflow drains backinto the storage tank through a check valve at the liquid inlet. As thetemperature of the LPG inside the primary heat exchanger increases, theLPG vaporizes and flows through the liquid carryover prevention switchinto the secondary heat exchanger 18. The secondary heat exchangerutilizes the rising flue gases produced by the IR burners to recoverthermal energy and increases the thermal efficiency of the IR vaporizer.The exhaust stack 42 vents the flue gasses. The vaporized LPG continuesto flow through the vapor outlet 20, where the temperature switchcontinually monitors output temperature. Once the vaporized LPG iswithin the specified temperature limits, the switch closes the burnercontrol valves on the IR burners to maintenance levels. Residual heatinside the heat exchangers continues to vaporize the remaining LPG,until the temperature at the outlet drops below the specified levelagain, at which point the burner control valves are opened again. Thesupply of LPG is replenished through the solenoid valve at the liquidinlet, which stays open while control voltage is applied, and the liquidcarryover prevention switch does not detect liquid. Should operatingpressure rise above the design pressure, the LPG vapor is automaticallyvented through the pressure relief valve stack 40.

The IR burners possess standing pilot lights and are fueled by a smallportion of the vaporized LPG. Fuel line valve 22 is located at the vaporoutlet and allows fuel flow to fuel line 24A. The fuel line feeds intopressure regulator 26, which reduces the pressure of the LPG vapor fromthe vaporizer operating pressure to the pressures required by the IRburners. Fuel lines 24B and 24C lead to the IR burners. Drip leg 28allows the collection and removal of condensate from the fuel lines.

ADVANTAGES OF THE INVENTION

From the description above, a number of advantages of the IR LPGvaporizer become evident:

a) The employment of IR radiation to heat the heat exchanger directlyrather than using a heat transfer medium greatly increases theefficiency of the heat exchange, since the number of transactionsrequired to transmit the heat energy into the LPG, and thereby thenumber of times their inherent inefficiencies are incorporated into thetransfer, has been reduced.

b) No liquid heat transfer media are used, reducing both weight andrequired footprint of the IR LPG vaporizer.

c) The design of the IR LPG vaporizer is simpler and less complex thanknown designs of gas fueled vaporizers, since no primary heat transfermedium needs to be controlled or contained.

d) The IR burners used in the vaporizer are fueled with a portion of thevaporized LPG, making the IR LPG vaporizer independent from externalfuel sources.

e) The secondary heat exchanger increases the overall efficiency of theIR LPG vaporizer by utilizing heat from the flue gasses that wouldotherwise be lost.

f) The IR LPG vaporizer does not rely on external sources of electricityto run or control vaporization.

CONCLUSION, RAMIFICATION, AND SCOPE OF INVENTION

This has been a description of examples of how the invention can becarried out. Those of ordinary skill in the art will recognize thatvarious details may be modified in arriving at other embodiments, andthese embodiments will come within the scope of the invention. Thesemodifications include but are by no means limited to the following:

-   -   increasing or decreasing the number of heat sources or heat        exchangers;    -   changing the type of heat exchangers;    -   changing the arrangement of heat sources, heat exchangers,        pipes, and/or controls;    -   using a different control method, for example using an external        power supply to power a Programmable Logic Controller or other        electronic control system; or    -   removing the secondary heat exchanger entirely, relying solely        on the IR heat source.

Thus the scope of the invention should be determined by the appendedclaims and their legal equivalents, rather than by the examples given.

1. A method of vaporizing liquefied petroleum gas, the methodcomprising: a) using a device for emitting infrared radiation to heatsaid liquefied petroleum gas, b) using a device for absorbing saidinfrared radiation, and c) using said device for containing saidliquefied petroleum gas, and d) transferring said absorbed infraredradiation to said liquefied petroleum gas whereby said liquefiedpetroleum gas is caused to vaporize.
 2. The method of claim 1 whereinthe amount of said infrared radiation is controlled by means of atemperature switch operating a burner control valve.
 3. The method ofclaim 1 wherein the introduction of said liquefied petroleum gas intothe primary heat exchanger is controlled by means of a solenoid valve.4. A method of improving the thermal efficiency of infrared liquefiedpetroleum gas vaporizers, that method comprising: a) using a device forabsorbing and transferring thermal energy, b) positioning said device inthe stream of flue gas produced by said vaporizer, c) causing saiddevice to absorb thermal energy from said flue gasses and transferringsaid thermal energy to said liquefied petroleum gas vapors containedwithin said device, whereby a greater percentage of available thermalenergy is transferred to said liquefied petroleum gas vapors, increasingthermal efficiency.
 5. A method of preventing the carryover of liquidsin vapor streams produced by liquefied petroleum gas IR vaporizers, thatmethod comprising: a) using a float switch to detect the presence ofliquid in said vapor streams, b) positioning said float switch betweenprimary and secondary heat exchangers, substantially upstream of a vaporoutlet from said vaporizer, c) using said float switch to operate adevice for controlling introduction of liquefied petroleum gas into saidvaporizer, d) causing said float switch to close said device when liquidis detected in said vapor stream, whereby the injection of liquid intothe downstream vapor supply of said vaporizer is prevented.
 6. Themethod of claim 5 wherein said float switch operates a solenoid valve.7. A liquefied petroleum gas vaporizer comprising an infrared burnerdirectly heating a primary heat exchanger containing liquefied petroleumgas and a secondary heat exchanger being heated by the flue gassesproduced by said burners.
 8. The vaporizer of claim 7 wherein a floatswitch is used to prevent the introduction of liquid into the producedvapor stream of said vaporizer.
 9. The vaporizer of claim 7 wherein atemperature switch controls said burner.